1. Field of the Invention
The present invention relates to a fundus camera provided with a light-emitting diode (LED) as a light source to illuminate a fundus of a subject's eye.
2. Description of the Related Art
A halogen lamp that emits a fixed light as an observation light source has been used as a light source of a fundus camera and a xenon tube that emits a pulsed light has been used as a photographing light source. In recent years, with higher intensity of white LEDs, lighting apparatuses using, instead of a fluorescent lamp or an incandescent lamp, a white LED with a low heating value and less power consumption as a light source are increasingly used.
Also in the field of the fundus camera, a fundus camera using a white LED as an illumination light source is proposed. A fundus camera discussed in Japanese Patent Application Laid-Open No. 2007-29726 uses a plurality of white LEDs arranged in a ring shape as an illumination light source. LEDs having a plurality of different wavelengths are used, which include at least one LED including white, green, blue, and infrared, and further using at least one LED as a flash light source.
According to Japanese Patent Application Laid-Open No. 2006-174984, a luminous flux is emitted from a plurality of white LEDs arranged in a ring shape as an illumination light source of a fundus camera toward a concave-shaped diffusion reflector and a diffuse-reflected luminous flux is extracted from a ring-shaped opening to generate a uniform illumination light. The plurality of LEDs include a plurality of luminescent colors and further include a white LED and an infrared LED, which are switched alternately according to a photographing mode.
According to Japanese Patent Application Laid-Open No. 2007-29726, when the plurality of white LEDs are arranged in a ring shape, it is difficult to arrange the LEDs without gapping and it is also difficult to form a uniform illumination light, so that an obtained eye fundus image is not uniform in illumination.
According to Japanese Patent Application Laid-Open No. 2006-174984, a concave-shaped diffusion reflector is needed to form a uniform illumination light and thus, a problem that the illumination light source becomes more complex, larger, and more expensive occurs. Further, there is a problem that a luminous flux is diffuse-reflected by a diffusion reflector, thereby causing a loss of quantity of light.